1. Field of the Invention
The present invention relates to a support frame, and more particularly to a vertically adjustable support frame that is selectably raised and lowered by extending and retracting at least one articulating structure.
2. Description of the Related Art
Typically, height and angle adjustable beds are used by medical institutions, such as hospitals and nursing homes. The beds usually include a bed frame and an articulating mechanism for lowering the bed frame to a low position and raising the bed frame to a high position so that it may be used as a gurney or at any height in between. As a result, a patient can be transferred by merely sliding the patient from one gurney to another or a chair.
It is known to have height and angle adjustable beds that may be lowered to a fully lowered position near the floor; however, such beds usually require a mechanical or hydraulic compression assist mechanism or high-power hydraulic lift mechanisms to lift the bed from the fully lowered position. For example, U.S. Pat. No. 6,405,393 (“the '393 patent”) incorporated by reference herein, discloses a spring assist mechanism that allows a height adjustable bed to raise from a fully lowered position. The '393 patent describes the increase in force necessary to raise the bed from the fully lowered position. This is because as the angle between the linear actuator and the bed frame in the bed shown in the '393 patent approaches zero, the cosine of that angle also approaches zero. As the cosine of the angle approaches zero, the resultant lift component, or vertical component, of the actuator force also approaches zero. The actuator is therefore at a mechanical disadvantage when the cosine of the angle approaches zero. One way to overcome such a limitation is to use multiple actuators, or an actuator having a relatively large force. Such an approach can be undesirably expensive.
Further, a mechanical or hydraulic compressive assist mechanism may be used to overcome the mechanical disadvantage. However, such components may fail unexpectedly. In addition, when such mechanisms fail, time delay, damage or injury may occur. Thus, it would be desirable to eliminate any need for mechanical and hydraulic compressive assist mechanisms.
Presently, to achieve a low bed position, one must also accept a mechanical disadvantage. Further, elimination of the mechanical disadvantage requires that the cosine of the angle between the actuator and bed frame not approach zero, and accordingly that the bed not be lowered to the desired position. Thus it would be desirable to achieve a low bed position while simultaneously avoiding a situation where the cosine of the angle between the bed frame and linear actuator approaches zero.
A still further disadvantage yet of some existing angle adjustable beds that have two motors is that the motors can get out of synchronization. In this regard, either motor may raise or lower a respective end of the bed at a different rate. This could jeopardize the health and safety of any person on the bed. Further, such a drawback could make transport during raising and lowering of the bed impractical and hazardous.
A still further disadvantage yet of existing angle adjustable beds is that they may require an undesirably large amount of swing to reposition the bed from the lowered position to the raised position. The swing occurs as a result of the support frame of the bed moving forward or rearward relative to the wheels. A large swing is disadvantageous for several reasons. First, having bed frame move forward or rearward relative to the wheels changes the center of gravity of the bed. The larger the swing, the larger the change in the center of gravity of the bed. Second, with the ever increasing pressure to reduce room size and to fit more items into existing rooms, there is a sizable disadvantage to a bed that requires a relatively large amount of swing to raise to the raised position.
A still further drawback yet is that some beds require three or more casters at each end of the bed to provide a stable structure. This leads to an undesirable number of components. Alternatively, some beds have a stabilizing rod extending between the casters from the front to the rear of the bed. These stabilizing rods can interfere with and limit the use of items such as over bed tables, patient lifts and the like.
Thus there exists a need for a support frame that solves these and other problems.